The U.K. failed to find enough buyers for 1.75 billion pounds ($2.55 billion) of bonds for the first time in almost seven years as debt investors repudiated Prime Minister Gordon Brown’s plan to stem the worst economic crisis in three decades.

Gilts slumped after the London-based Debt Management Office, which manages bond auctions on behalf of the Treasury, said investors bid for 1.63 billion pounds of the 40-year securities. The last time the U.K. government was unable to attract enough investors was in 2002 when it tried to sell 30- year inflation-protected bonds. The yield on the 4.5 percent gilt due 2049 rose 10 basis points to 4.55 percent.